Plasma arc torches are widely used in the cutting and marking of materials. A plasma torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling fluids (e.g., water), and passages for arc control fluids (e.g., plasma gas). The torch produces a plasma arc, a constricted ionized jet of a gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen) or reactive (e.g., oxygen or air). During operation, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode). Generation of the pilot arc can be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or by means of any of a variety of contact starting methods.
In a fluid-injection plasma system, cut quality (e.g., the quality of angles, dross, and edge color) is sensitive to the flow rate of the shield fluid. The flow rate of shield fluid can vary for different reasons, for example as the elevation of the fluid selection console changes relative to the torch. In some cases in which water is the shield fluid, the fluid flow rate can change by up to 0.5 gallons per hour for every linear foot of elevation change. Such variation can in turn cause significant variation in cut quality. What is needed is a plasma arc cutting system that is desensitized to external pressure changes in the system (e.g., caused by elevation changes of the fluid selection console), thereby ensuring consistent cutting quality.